A hose coupling or hose mouthpiece, such as used in automotive hydraulic brake lines have been used by considering its features of detachability, reliability and leakproof. A conventional hose coupling comprises a tubular nipple portion having an axial bore, a tubular sleeve portion axially extending over the nipple portion, and a head portion, to one end of which one ends of the nipple portion and the sleeve portion are joined such that the axial bore is provided therethrough. In general the head portion is internally provided with a female thread by which the hose coupling is connected to a nozzle member. These kinds of hose coupling or hose mouthpiece have been produced according to a variety of methods, such as (a) cutting each portion of the hose coupling from a blank material, (b) producing a nipple portion, a sleeve portion and a body portion including a head portion separately and securing the separate parts together by brazing, (c) securing a body portion including a head portion and a separate sleeve portion together by caulking.
According to the first method, however, there are disadvantages in that it is not suitable for mass production because cutting generates a large quantity of chips and its relatively slow operation speed results in high cost. In addition to that, it causes lack of stability in finished dimensions.
The second method of brazing has an advantage in mass production. FIG. 1 shows an example of a conventional hose coupling produced by this method. The hose coupling 10 comprises an inner tube 11 and an outer tube 12 separately. The outer tube 12 includes a head portion 13, a sleeve portion 14 extending from one end of the head portion 13, a female thread 15 internally provided on the side wall of a bore 22 produced on another end of the head portion 13, an annular groove 16 and a flange portion 17 in its periphery. The inner tube 11 comprises a conical seal portion 18, a nipple portion 19, and a flange portion 23 such that an axial bore 20 is provided therethrough, as shown in FIG. 2A. The inner tube 11 is formed by plastic deformation using a former, while the outer tube 12 is usually produced from a round rod or pipe by cutting. The inner tube 11 is inserted into an inner bore 24 of the outer tube 12 (see FIG. 2B) such that the flange portion 23 fits to the inner bore 24, and secured to the outer tube 12 by brazing using copper solder, etc. The sleeve portion 14 and the nipple portion 19 produce a cylindrical receiving pocket 21 in which an end of a hose member is inserted and secured by crimping. FIG. 3 also shows a similar conventional hose coupling, wherein like parts are indicated by like reference numerals as used in FIG. 1. In this case, a step-like annular groove 36 is provided in the periphery of a head portion 13.
Since brazing is done at higher temperature than a melting point of a solder, it is done at 1,100.about.1,150.degree. C. for copper solder, for example.
According to the second method, however, there are disadvantages set out below.
(1) cutting is necessary to form the nipple portion 11. It generates chips as wastes and the yield of production is not so good.
(2) the nipple portion 19 is so small in its diameter and so long that it takes longer time to produce the axial bore 20. The bore may be oblique, which results in a deterioration of crimping conditions.
(3) at least inner tube 11 and outer tube 12 must be produced separately. The flange portion 23 and the inner bore need to be made in precise dimensions to be fit to each other securely and brazed. It requires more stages for manufacturing and quality management and is not cost-effective.
(4) the heat of brazing anneals the nipple portion 19 and makes it softer. As a result, the nipple portion 19 is easy to collapse when the sleeve portion 14 is crimped together with the hose member.
(5) fluid leak may happen due to an incomplete seal or inappropriate brazing of a joint, such as skipping the stage and falling off of a solder.
(6) the nipple portion 19 may be eccentrically fitted into the inner bore 24, which results in difficulty in inserting an end of a hose member.
According to the third method, securing a body portion and sleeve portion together by caulking, it has been considered that it has advantages of less stages of manufacture, less possibility of nipple collapse and low cost. However, there is disadvantage in that it is more likely that leak of fluid from a joint than in the brazing method, and it does not seem to be practically implemented.
On the other hand, besides the conventional hose couplings having a female thread shown in FIGS. 1 and 3, other types of hose coupling are known.
FIG. 4 shows a conventional hose coupling having a male thread 40, which also comprises an inner tube 41 as a nipple portion, and an outer tube 42, separately. The outer tube 42 includes a head portion 43, a sleeve portion 44 extending from one end of the head portion 43, a male thread 45 externally provided in the periphery of the head portion 43, a flange portion 47 in its periphery. One end of the inner tube or nipple portion 41 is inserted into a bore 46 such that an axial bore 20 is provided therethrough.
FIG. 5 shows a conventional hose coupling having an eye ring 53a, which comprises a inner tube or nipple portion 59, a sleeve portion 54, and a head portion 53. The head portion 53 includes an eye ring 53a which provides an eye opening 53b, and a neck portion 53c to join the eye ring 53a to the sleeve portion 54. One end of the nipple portion 59 is inserted into a hollow portion of the neck portion 53c and joined thereto. FIG. 6 shows a conventional hose which comprises a nipple portion 69, a sleeve portion 64 and a flat head portion 63 having a rectangular shape cross-section. The flat head portion 63 is provided with an opening 67 and a female thread 65 at one end of an axial bore 66, which is bent in L shape inside the flat head portion 63. The nipple portion 69 and the sleeve portion 64 are co-axially attached to a surface on which an opening of another end of the bore 66 is located.
Regardless these variations of head portions, the sleeve portion and nipple portion need to have a different hardness. If sleeve portion is harder than a certain hardness, it may crack due to a crimping work. On the contrary, if the nipple portion is not harder than a certain hardness, it may collapse due to the crimping work, resulting in the possibility of seal deterioration, or deviation of inner diameter of a hose member. According to the conventional hose couplings, the inner tube or nipple portion is made of relatively harder material like chromium-molybdenum steel, while the outer tube or sleeve portion 91 is made of steel. Therefore, there is a disadvantage in that mechanical strength of a female or male thread is insufficient to ensure leakproof of joint between the hose coupling and a nozzle member. Because the female or male thread is internally or externally formed in or on a head portion by like machining, which is made of the same material as the outer tube or sleeve portion, the female or male thread may be not hard enough to avoid breakage or to transfer sufficient stress to a seal portion of the hose coupling.